// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_EVENTS_EVENT_REWRITER_H_
#define UI_EVENTS_EVENT_REWRITER_H_

#include "base/memory/scoped_ptr.h"
#include "ui/events/events_export.h"

namespace ui {

class Event;

// Return status of EventRewriter operations; see that class below.
enum EventRewriteStatus {
    // Nothing was done; no rewritten event returned. Pass the original
    // event to later rewriters, or send it to the EventProcessor if this
    // was the final rewriter.
    EVENT_REWRITE_CONTINUE,

    // The event has been rewritten. Send the rewritten event to the
    // EventProcessor instead of the original event (without sending
    // either to any later rewriters).
    EVENT_REWRITE_REWRITTEN,

    // The event should be discarded, neither passing it to any later
    // rewriters nor sending it to the EventProcessor.
    EVENT_REWRITE_DISCARD,

    // The event has been rewritten. As for EVENT_REWRITE_REWRITTEN,
    // send the rewritten event to the EventProcessor instead of the
    // original event (without sending either to any later rewriters).
    // In addition the rewriter has one or more additional new events
    // to be retrieved using |NextDispatchEvent()| and sent to the
    // EventProcessor.
    EVENT_REWRITE_DISPATCH_ANOTHER,
};

// EventRewriter provides a mechanism for Events to be rewritten
// before being dispatched from EventSource to EventProcessor.
class EVENTS_EXPORT EventRewriter {
public:
    virtual ~EventRewriter() { }

    // Potentially rewrites (replaces) an event, or requests it be discarded.
    // or discards an event. If the rewriter wants to rewrite an event, and
    // dispatch another event once the rewritten event is dispatched, it should
    // return EVENT_REWRITE_DISPATCH_ANOTHER, and return the next event to
    // dispatch from |NextDispatchEvent()|.
    virtual EventRewriteStatus RewriteEvent(
        const Event& event,
        scoped_ptr<Event>* rewritten_event)
        = 0;

    // Supplies an additional event to be dispatched. It is only valid to
    // call this after the immediately previous call to |RewriteEvent()|
    // or |NextDispatchEvent()| has returned EVENT_REWRITE_DISPATCH_ANOTHER.
    // Should only return either EVENT_REWRITE_REWRITTEN or
    // EVENT_REWRITE_DISPATCH_ANOTHER; otherwise the previous call should not
    // have returned EVENT_REWRITE_DISPATCH_ANOTHER.
    virtual EventRewriteStatus NextDispatchEvent(
        const Event& last_event,
        scoped_ptr<Event>* new_event)
        = 0;
};

} // namespace ui

#endif // UI_EVENTS_EVENT_REWRITER_H_
